How is Cancer Diagnosed?

The moment someone receives a cancer diagnosis can seem like the starting line of a long and grueling marathon. It is often some of the most difficult news that someone can receive in their lifetime, and the diagnosis itself has a massive impact on what kinds of care and treatment a patient will receive. For this reason, it is essential that an individual’s cancer journey starts with as specific and as accurate a diagnosis as possible. Not all cancers are diagnosed in the same way, but this page will discuss some of the more common methods.

In most cases, diagnosing cancer involves more than one step or investigation. Often, a patient will present to care with a symptom suggestive of cancer, or a screening test result that necessitates further work up. Sometimes, a patient undergoes investigations such as imaging for an entirely unrelated problem, and evidence of cancer is found incidentally, or by accident. In all these cases, many doctors will start in the same place: by talking to you!

Collecting a personal and family history from a patient can be invaluable in narrowing down possible diagnoses. Everything from a patient’s current symptoms to their past diagnoses, and their habits (such as drinking alcohol and smoking) can give hints to what conditions or diseases they are more susceptible to. Knowing what diagnoses family members have received is also helpful, as certain cancers can have genetic components passed down from parent to child. To highlight the importance of this type of context, I offer the example of 2 patients, both presenting with a new-onset cough. The first is 12, has never smoked, and coughs when he runs during gym or other exercise. Both his brothers and his mother have asthma. The second is a 65 year-old male who has smoked a pack of cigarettes a day for the past 50 years, and now presents with cough, chest pain, shortness of breath as well as bony pain and weight loss. From their stories alone, one of these patients is far more likely to have cancer than the other.

Physicians will also perform a physical examination to determine if there are any physical signs of cancer or other disease. Sometimes, a cancerous lump is palpable. Other times more systemic signs of cancer can be noted. Not uncommonly, cancer isn’t apparent at all on physical exam. That is why it is important that suspicious symptoms or findings be investigated further, even if it doesn’t seem like anything is overtly wrong. Below, we will discuss briefly some of the most common investigations used to detect and diagnose cancer.

Imaging:

Today, there are several forms of medical imaging that can be used to essentially ‘take pictures’ of the inside of your body. To the untrained eye, these images can often seem more like abstract art than anything useful (a thought that inspired the artwork at the top of this page), but medical professionals trained to read these images can use them to detect tumors or other abnormalities suggestive of cancer. The specific test used depends on the patient, the area of the body being examined, and what kind of information a physician is hoping to find. You could write a book on all the specifics of each one of these modalities – and people have! But from a patient’s perspective, many of them can seem very similar. Imaging tests include X-rays, CT scans, MRI, PET scans, nuclear scans, bone scans, ultrasound, and more. I will not bore you with the details of how these modalities work, but if you are interested the National Cancer Institute provides an excellent overview, as does the Canadian Cancer Society!

Laboratory Tests:

While imaging can provide high-level information about where a cancer may be, its size, and whether it has spread, it is also very useful to gather information at a much smaller – or cellular level. To do this, a physician may require a blood sample to examine for signs of cancer. Helpful blood tests include a CBCd (or complete blood count and differential), blood chemistry tests (which can look for specific electrolytes, proteins, fats, sugars, and metabolites in the blood). Specific cancer markers, such as CEA, CA125, and even PSA can also be a helpful addition to other investigations for certain cancers. But they will rarely provide enough information on their own to warrant a diagnosis. In some cases, cytology (which takes a look at cells from a sample such as a swab of the cervix or sputum coughed up from your lungs) can also be helpful. And in the cases of certain cancers, genetic testing can be helpful in better characterizing a cancer and directing treatment.

Biopsy:

While not all cancers require biopsy for diagnosis, most do. Biopsy is the process of taking a small sample of a larger tissue, so that it can be further examined. This can look very different depending on the tissue in question. For example, sometimes biopsies can be done with just a needle and local anesthetic. Others may require more general anesthesia and endoscopy, such as gastroscopy or a colonoscopy. Others still may require surgery. Regardless, the result is similar: a small sample of suspicious tissue is obtained. In many cases, a specialist called a pathologist will stain the tissue with specific dyes and examine it under a microscope. Throughout medical school, I always struggled to make sense of these stains. To me, the purple-and-pink-stained cells all-too-often looked like random inkblots, or even the patterns on the wings of a butterfly (a concept which I captured in the art below). Clearly, I wasn’t cut out to be a pathologist. But with an incredibly trained eye, and a toolkit of other testing, pathologists can distinguish cancer cells from healthy cells, and are often able to make a final diagnosis based on the tissue taken in a biopsy. They can also provide useful information about the cancer cells, including their grade (or how different they are from their healthy counterparts), and the arrangement of the cells. Certain molecular characteristics can also be reported based on pathology, for example the presence of estrogen or progesterone receptors in breast cancer. This is important for certain cancers, as it guides treatment.